Generally, a piezoelectric vibrator such as a crystal oscillator is configured by a piezoelectric element being accommodated in a package. External connection electrodes are provided on an outer surface of the package. The external connection electrodes are electrically connected to electrodes inside the package. The piezoelectric element is accommodated in the package in a state where electrodes of the piezoelectric element are connected to the electrodes inside the package.
Generally, the piezoelectric element is provided with two electrodes, which are connected to two electrodes inside the package by an electrically conductive adhesive, respectively. In order to connect the electrodes by the electrically conductive adhesive, first, a fixed amount of the electrically conductive adhesive is applied onto each of the electrodes inside the package, and, then, the electrically conductive adhesive is cured after placing the electrodes of the piezoelectric element on the applied electrically conductive adhesive. That is, the piezoelectric element is accommodated in the package in a state where the electrically conductive adhesive is provided between the electrodes of the piezoelectric element and the electrodes inside the package.
When the electrodes of the piezoelectric element and the electrodes inside the package are joined by the electrically conductive adhesive as mentioned above, there may occur a problem in that short-circuiting occurs due to the electrically conductive adhesive flowing to other parts or running out of the electrodes or an oscillation frequency of the piezoelectric element is changed.
Thus, Japanese Laid-Open Patent Application No. 2000-124761 suggests a piezoelectric oscillator package, which has a concave portion on an inner wall of a ceramic container and an a ceramic substrate is fixed to the ceramic container by fitting an end of the ceramic substrate into the concave portion. In this piezoelectric oscillator package, through holes are formed in the ceramic substrate so that the ceramic substrate is fixed to the ceramic container by filling an electrically conductive adhesive into the through holes.
Japanese Laid-Open Patent Application No. 2007-288644 discloses a piezoelectric substrate having a structure in which a concave portion or a through hole is provided between a part to be joined by an electrically conductive adhesive and part not to be joined by the electrically conductive adhesive in order to absorb a portion of the electrically conductive adhesive which runs out of the part to be joined by the electrically conductive adhesive.
Japanese Laid-Open Patent Application No. 8-181407 suggests a structure for mounting a mount part to a printed wiring board in which an electrically conductive paste is filled into through holes formed in the printed wiring board so that the mount part is mounted by inserting electrodes of the mount part into the electrically conductive paste in the through holes.
Further, Japanese Laid-Open Patent Application No. 7-66670 discloses a piezoelectric vibrator having a structure in which a slit is provided in each of a plurality of support plate extending from a support table so that the piezoelectric vibrator is mounted by side ends of a piezoelectric substrate being fitted into the slits.
In a case where an electrically conductive adhesive is applied onto electrodes of a package by using a dispenser, the electrically conductive adhesive in liquid form is dripped onto each electrode from a tip of a nozzle of the dispenser. In this regard, there may be a variation in an amount of drip of the electrically conductive adhesive and a position of the drip of the electrically conductive adhesive. FIG. 1 is a plan view illustrating a state where an electrically conductive adhesive is dripped onto two electrodes in a package by using a dispenser. It can be appreciated from FIG. 1 that, due to such a variation in the amount of drip and the dripped position, a size and a position of the drips of the electrically conductive adhesive 6 on the two electrodes 4-1 and 4-2 in the package 2 vary greatly.
If the position and the amount of the electrically conductive adhesive 6 vary as illustrated in FIG. 1, a problem may occur that the oscillation frequency of the piezoelectric element is unstable or the piezoelectric element cannot generate oscillation. Additionally, an oscillation frequency characteristic may be changed due to a change in a stress distribution generated in the piezoelectric element in association with aging of the electrically conductive adhesive 6.
Thus, it is desirable to achieve a mounting structure in which positions at which the electrodes of the piezoelectric element are in contact with the electrically conductive adhesive are fixed and the contact areas are also fixed even if there is a variation in the drip amount and the drip position in a case where the electrically conductive adhesive if applied by a dispenser.